In a digitally controlled inkjet printing system, a receiver media (also called a print medium herein) is directed through a series of components. The receiver media can be a cut sheet of media or a continuous web of media. A web or cut sheet transport system physically moves the receiver media through the printing system. As the receiver media moves through the printing system, liquid (e.g., ink), is applied to the receiver media by one or more printheads through a process commonly referred to as jetting of the liquid. The jetting of liquid onto the receiver media introduces significant moisture content to the receiver media, particularly when the system is used to print multiple colors on a receiver media. Due to the added moisture content, an absorbent receiver media expands and contracts in a non-isotropic manner, often with significant hysteresis. The continual change of dimensional characteristics of the receiver media can adversely affect image quality. Although drying is used to remove moisture from the receiver media, drying can also cause changes in the dimensional characteristics of the receiver media that can adversely affect image quality.
FIG. 1 illustrates a type of distortion of a receiver media 3 that can occur during an inkjet printing process. As the receiver media 3 absorbs the water-based inks applied to it, the receiver media 3 tends to expand. When the direction of expansion is in a direction that is perpendicular to a media advance direction 4, it is referred to as expansion in the cross-track direction 7. Typically, the contact of the receiver media 3 with rollers 2 (or other components) in the inkjet printing system produces sufficient friction between the receiver media 3 and contact surface 8 that the receiver media 3 is not free to slide in the cross-track direction 7, even though the receiver media 3 is beginning to expand in that direction. This can result in localized buckling of the receiver media 3 away from the rollers 2 to create lengthwise flutes 5, also called ripples or wrinkles, in the receiver media 3. Wrinkling of the receiver media 3 during the printing process can lead to permanent creases in the receiver media 3 which adversely affects image quality.
Inkjet printheads are typically located and aligned over the receiver media 3 by a support structure. In some such systems, the support structure locates multiple printhead modules in two or more rows; the rows being substantially parallel to each other and aligned with the cross-track direction. To prevent the receiver media 3 from vibrating up and down in the print zone, the receiver media 3 is supported by a media guide surface that is aligned with the print line of each row of printheads. It is not uncommon for the bottom face of the support structure to become wet, for example due to condensation from the moist air produced by the printing process.
It has been found that under some printing conditions the flutes 5 in the receiver media 3 can be sufficiently tall that the top of the flutes 5 can contact the bottom surface of the support structure of the printhead. When this occurs, the printed ink on the flutes 5 can be smeared by the contact. Additionally, the moisture on the bottom of the support structure can be transferred to the receiver media 3. The result is a degradation of the print quality. As such, there is an ongoing need to provide inkjet printing systems and processes with the ability to effectively handle receiver media expansion associated with the absorption of water by the receiver media 3 in order to prevent the receiver media 3 from contacting the support structure so that good print quality can be maintained.